The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

As Ehrlich had imagined back in 1891, these blasts now begin to secrete the receptor into the blood. Freed from the B cell’s membrane and now floating in the blood, the receptor “becomes” the antibody.I And when the antibody is bound to its target, it can summon a cascade of proteins to poison the microbe and can recruit macrophages to devour, or phagocytose, it. Decades later, researchers demonstrated that some of these activated B cells don’t simply peter out. They persist in the body in the form of memory cells. In Thomas’s words, “The new cluster [of cells stimulated by the antigen] is a memory, no less.” Once the fulminant infection has ceased and the microbe cleared, some of these B cells become more quiescent, but they persist—finches huddled in the cave. When the body encounters the antigen again, the memory B cell is reactivated. It arises out of dormancy into active division to mature into an antibody-making plasma cell, thereby encoding an immunological memory. The locus of immunological memory, in summary, is not a protein that persists, as Ehrlich may have imagined. It is a B cell, previously stimulated, that bears the memory of the prior exposure.